Patent Document 1 discloses a projector that has a projection lens optical system, an automatic focal point detection device, and an angle detection device. The projection lens optical system projects an image on a screen. The projection lens optical system is able to move in the direction of the optical axis.
The automatic focal point detection device is provided with a photo-detection element for imaging the projected image. The automatic focal point detection device uses a photo-detection element to capture the image of the projected image on the screen while moving the projection lens optical system along the direction of the optical axis and detects as the focus position the position at which the high-frequency component of the image that was captured becomes a maximum. The automatic focal point detection device causes the projection lens optical system to move to the detected focus position.
The angle detection device is provided with a pair of line sensors that photo-detect image light from the screen. After the projection lens optical system has been moved to the focus position, the angle detection device uses the pair of line sensors to measure each of the distances from the projector to a plurality of sites of the projected image on the screen. The angle detection device then, based on the result of measuring the distance of each site, finds the angle of inclination of the optical axis of the projection lens optical system with respect to the screen and carries out trapezoidal distortion correction according to this angle of inclination.
After the trapezoidal distortion correction, the angle detection device again uses the pair of line sensors to measure each of the distances from the projector to the plurality of sites of the projected image on the screen. The angle detection device then, based on the results of measuring the distance of each site, moves the projection lens optical system to perform focus readjustment.